Method of refining vegetable and animal oils



United States Patent U.S. Cl. 260425' Claims ABSTRACT OF THE DISCLOSUREThe alkali refining of edible oils is carried out in the presence of aconcentrated, e.g. 25%30% or 40%, aqueous solution of a salt of amononuclear aryl or mononuclear alkyl aryl sulphonic acid in which thetotal number of carbon atoms of the alkyl chains is not greater than 4.The mixture resolves into a refined oil phase and an aqueous phasecontaining the soapstock. After separation, the soap is split byacidification and the resulting free fatty acids are recovered. Theaqueous residue is preferably recycled after crystallising out excessinorganic salts.

The present invention relates to an improved method of refiningvegetable, animal and marine oils and is a continuation-in-part of ourcopending application No. 340,804 filed Jan. 20, 1964 and now abandoned,which is itself a continuation-in-part of application No. 290,935 filedJune 27, 1963 and now abandoned.

Such oils are neutral glyceride esters of fatty acids, but duringextraction from their naturally occurring state some degradation of theoil occurs and the resulting crude oil contains free fatty acidsdissolved in the oil. The conventional method of refining such oilsinvolves treating the crude oil with an aqueous alkaline solution, suchas dilute sodium hydroxide or sodium carbonate, followed by severalwater washes and, if necessary, by an adsorptive bleaching process usingactivated earths. In some cases, a process of deodorisation is also usedin which steam or an inert gas is blown through the oil at an elevatedtemperature under vacuum. In this alkali refining process, the freefatty acids present in the crue oil are removed as soaps. This method ofrefining suffers from the inherent disadvantage that the soap forms amicellar solution in water which entrains appreciable quantities of theglyceride oil. Thus, not only is there a loss of the glyceride oil, butalso the fatty acids which may be recovered from the soapstock arecontaminated with considerable amounts of glyceride oil. Moreover therefining process takes several hours to complete if separation iscarried out by the usual gravity method.

Various methods have been proposed to reduce the losses of oil and/ orto improve the purity of the recovered oil and soapstock, e.g., U.S.Patents Nos. 2,225,575, 2,437,075, 2,551,496 and 3,065,249. All of theseproposed solutions have been partially or wholly unsatisfactory and oilrefiners have to accept that considerable oil losses will occur evenwith the most advanced of the prior oil refining techniques.

We have now found that the presence of a concentrated aqueous solutionof certain benzene or a'lkylbenzene sulphonat salts during the alkalirefining of the crude oil enables a much more rapid and completeseparation of the oil and soap layers to be achieved, with the resultthat the amount of oil entrained in the soap layer is greatly reduced.Moreover the presence of the sulphonate salts during refining reducesthe time required to secure adequate separation of the oil from the soaplayer to a matter of minutes. This is to be contrasted with the hoursrequired to secure a comparable separation when conventional refiningtechniques are used.

Where the original glyceride oil contains phosphatides, eg in the caseof soya bean oil, we have found that these are extracted into the theaqueous layer and can be recovered therefrom by known methods. Thephosphatides, e.g. lecithin, may be valuable by-products of the process.Furthermore, other polar bodies such as proteins, aldehydes andcolouring matter which are more hydrophilic than the glyceride oils butsomewhat less hydrophilic than the soaps, are also removed from the oilphase into the aqueous phase. Because of this the oils obtained by ourmethod are substantially equal in quality to oils obtained byconventional refining methods which involve purification in severalstages including alkali refining, adsorptive bleaching and de-odorising.By using our method it may be possible in some cases to reduce thenumber of refining stages to one.

The sulphonate salts for use in the invention are defined as monouuclearsulphonates of alkyl aryl sulphonates wherein the aromatic nucleus maycontain up to three alkyl substituents, and the total number of carbonatoms of all the alkyl substituents does not exceed four. Suchsulphonate salts include for example the alkalimetal or ammonium saltsof benzene, xylene, toluene, cymene and cumene sulphonic acids. Wherethe refined olis are intended for use in the preparation of foodstuffs,it is preferred to employ sulphonate salts which are substantially freefrom sulphone materials. Such sulphonefree sulphonate salts may bereadily obtained in known manner by preparing a crude sulphonic acid bythe action of sulphur trioxide on the appropriate hydrocarbon, quenchingthe reaction mixture, neutralising it with a base and subsequentlywashing the crude sulphonate salt with the hydrocarbon from which it hasbeen derived. Especially preferred sulphone-free hydrotropes for presentuse are those sodium xylene sulphonates sold by the applicants under thetrademark Halvopon Or.

The sulphonate salts for present use do not markedly depress the surfacetension of water and are not to be confused with the surface-activesulphonate salts, which contain long chain alkyl substituents. Thesurface-active sulphonate salts are not suitable for present use since,even when used in minor amounts, they bring about emulsification of theoil and soap layers and render it virtually impossible to recover anyoil from the refining mixture.

The concentration of the sulphonate salt during refining required toachieve the clean separation of the oil and soap layers will depend uponthe salt employed. As a general guide we have found that a concentrationof at least 30% by weight is required with most of the sulphonate saltsalthough cumene sulphonates are effective when used in a concentrationas low as 25%. There is no upper limit to the concentration of theaqueous sulphonate solution which is employed and saturated solutionsmay therefore be used. However, the optimum concentration is less thansaturation and is usually within the range 40 to 60%. The concentrationsreferred to above are based on the total amount of water present in therefining mixture. Since appreciable amounts of water are added with thealkali and since the oil may contain some water, the concentration ofthe aqueous solution of the sulphonate added to the refining mixture isusually Well in excess of the figures quoted above in order to achievethe desired concentration during refining. In some instances to achievethe desired concentration it may be necessary to add dry sulphonate saltto the refining mixture.

The amount of sulphonate salt, as opposed to the concentration of itsaqueous solution, required to bring about a satisfactory separation ofthe oil and soap layers will depend upon the amount of free fatty acidin the crude oil. The use of 2 to 6 times the weight of the free fattyacid in the crude oil usually provides satisfactory results.

The alkali used in the refining of the crude oil may be any of thesaponifying or non-saponifying alkalis in common use. It is preferred touse sodium hydroxide and/or sodium carbonate. The amount of waterpresent is determined by the amount of and concentration required forthe sulphonate salt, with the result that the alkali is usually presentinitially as a dilute aqueous soltion, for example a 20% solution. Asindicated above, the water added to the crude oil in the form of theaqueous alkali must be allowed for when calculating the concentration ofthe sulphonate solution which is to be added. In some cases it may benecessary to use comparatively concentrated aqueous alkali in order toavoid adding excessive amounts of wateuto the refining mixture. Owing tothe reduction in the viscosity of the soapstock using the sulphonatesalts, it is possible to reduce the excess of alkali used from theconventional 25% excess over that theoretically required to neutraliseall the free fatty acids in the crude to 10% or less.

The process of the invention is applicable to the treatment of a largevariety of crude oils and has the advantage that it can be used forrefining oils which contain more than the normal amount of fatty acidsand which would not be worth refining, or would be impossible to refine,by conventional methods owing to the excessive loss of oil or theimpossibility of breaking the soap/oil emulsions formed during refining.In particular, tallow oils, which contain as much as 25 fatty acids, canbe refined by the method of our invention with very little loss ofglyceride oil.

One method of extracting vegetable oils is to digest crushed seeds witha hydrocarbon solvent, for example hexane. We have found that theresulting solution of the oil is excellently suited to the process ofthe invention, since the separation into the aqueous layer and the oillayer is even quicker than in the case when the oil undissolved inhydrocarbon is used. It is to be understood that in the description ofthe invention and the claims herein, the term oil includes, where thecontext permits, solutions of oil in hydrocarbon solvents.

In view of the short time required for separation of the aqueous andsolvent phases, the use of hydrocarbon solu tions of the oils lendsitself with especial advantage to the operation of the invention as acontinuous process, though the invention is also applicable to batchoperations.

The refining of the crude oil may be carried out in the normal manner.The oil may be admixed with the alkali and subsequently with thesulphonate salt or in the reverse order. More commonly the sulphonatesalt and alkali solutions may be premixed and the mixture then fed tothe crude oil.

During the refining of the oil soaps are formed by the action of thealkali on the free fatty acids in the crude oil. After refining has beencompleted, the refining mixture is allowed to separate into an upper oillayer and a lower aqueous soap layer. The separation of the layers maybe aided by, for example, centrifuging or other mechanical means.

If an even higher degree of purity in the oil is req ired, the oillayer, after separation of the aqueous layer,

may be treated with a further small qauntity of sulphonate salt inaqueous solution and the two layers formed allowed to separate. Thesecond aqueous layer is separated off and may be combined with thatoriginally obtained if desired. The oil layer, after a wash with water,is dried under vacuum to obtain substantially pure glyceride oil.

The aqueous layer or layers obtained from the refining of the crude oilcomprise a solution of the fatty acid soaps in the sulphonate saltsolution. The fatty acid values may be recovered from such a solution bytreatment with a mineral acid, such as sulphuric acid. Acidification ispreferably carried out to give a pH value of from about 4 to about 5.Often the fatty acids, especially if they are of comparatively lowpolarity, will separate out after acidification to form an upper fattyacid layer which may be recovered, for example, by decantation but inthe case of acids of higher polarity it may be necessary to dilute thesulphonate salt in order to render the acids insoluble. Dilution of theacidified aqueous layer thus offers a simple and convenient method forseparating out the liberated fatty acids. It will be appreciated thatthe use of a sufiiciently dilute mineral acid will achieve bothacidification and dilution.

After liberation and recovery of the fatty acids from the aqueous layer,the residual aqueous solution may be discarded or recycled for furtheruse since it contains the sulphonate salt. The recycled aqueous solutionalso contains appreciable quantities of alkali-metal salts of themineral acid used to liberate the fatty acids. The presence of excessivequantities of these salts may prove detrimental in the refining processand the amount present in the recycling aqueous solution is preferablymain tained at a low level. We have found that the solubility of sodiumsulphate in sodium sulphonate solutions is comparatively low andtherefore that, upon cooling of the recycling aqueous solution, a majorproportion of the sodium sulphate therein crystallises out and can beremoved, for example by filtration or centrifuging. The recyclingaqueous solution is usually too dilute for direct reuse in the refiningof further crude oil and it is then concentrated to approximately thelevel required for reuse. Conveniently this concentration is carried outbefore the mineral acid salts are separated. If required, additionalquantities of sulphonate salt may be added to the recycling aqueoussolution in order to make up any losses which may have occurred duringthe process. Furthermore, other impurities such as glycerol, or usefulbyproducts such as phosphatides may accumulate in the recycling aqueoussolution and it may be desirable to remove these in known manner, or todiscard the recycling solution.

Although the fatty acid mixture obtained by acidification of the aqueouslayer derived from the original alkali treatment is comparatively pure,it generally contains a residue of glyceride oil. According to a featureof the invention the process for recovering the fatty acids justdescribed is modified so as to give a fatty acid of improved purity. Theaqueous layer derived from the original alkali treatment is boiled withat least sufficient alkali to hydrolyse the glyceride oil therein togive a further quantity of fatty acid soap and glycerol; the mixture isacidified with a mineral acid to hydrolyse the soap; the resultingmixture is allowed to form two layers; and the lower, aqueous layer isremoved to leave a fatty acid layer of improved purity. It will beunderstood that the aqueous layer used as starting material for thisprocess contains the sulphonate salt originally present during therefining of the crude oil. The presence of the sulphonate salt isessential to the success of the process since without it, boiling of themixture would be a difiicult or impossible task owing to foaming causedby the soap, this foaming being wholly or largely prevented by thesulphonate salt. All the alkali necessary for the process of theinvention may be provided by adding a sufiicient excess of aikali in theoriginal treatment of the raw glyceride oil.

Alternatively some or all of the alkali may be provided separately afterthe initial refining process.

In carrying out this modified process just described, the original oiland acid mixture may first be treated as before, but with approximatelytwice the amount of alkali required to saponify the acids present, inthe presence of the sulphonate salt. The resulting mixture separatesinto an upper purified oil layer and a lower aqueous layer, whichcontains the saponified acids, sulphonate salt, excess alkali and someentrained glyceride oil. This aqueous layer is run off and boiled forabout one hour. At this temperature and time the alkali present splitsthe glyceride oil. If necessary, further alkali may be added at thisstage in order to give an excess calculated on the glyce-ride which ispresent. The aqueous layer is then treated as before to liberate thefatty acids, and to recover the sulphonate salt solution, which may berecycled. Hence, the process as a whole lends itself to continuousoperation.

As indicated above, it may be necessary to add further sulphonate saltto the recycling aqueous solution in order to make up any losses whichmay occur in the process. The point at which the additional requiredsulphonate salt is added to the recycling solution is comparativelyunimportant and this addition may in fact be made before or during theacidification of the soap layer to liberate the free fatty acidstherefrom.

The process of the invention will now be illustrated by the followingExamples, in which all parts are given by weight:-

In order to assess the results of the processes described, we quote therefining factors of these processes, since this is the criterion bywhich oil refiners judge the value of a refining operation. The refiningfactor is the proportion of the total weight of substance removed fromthe oil to the weight of free fatty acid originally present in the oil,and the ideal to be aimed at is a factor of unity.

EXAMPLE 1 100 parts of soya bean oil (acid value 2.2 mgs KOH/ g.) washeated to 95 C. To the hot oil was added 7 parts of sodium xylenesulphonate (SXS) in aqueous solution and an aqueous solution of causticsoda in an amount sufficient to give a excess based on the acid value ofthe oil. The amount of water in these solutions was enough to give a 40%solution of the SXS. The mixture was stirred and then allowed to settle.After 30 minutes the aqueous layer was separated, the oil was washed asecond time with 30% SXS, separated, washed with water and then driedunder vacuum at a temperature of 95 C. The combined aqueous layers weretreated with sulphuric acid to liberate the fatty acids. After removalof the fatty acids, the sodium sulphate was crystallised out andfiltered off to give a solution of SXS for reuse. The experiment wasrepeated except that the SXS solution was not present during refining. 8hours were required for the separation. The observed results are shownin Table 1.

XS Based Weight, AcidValue, Saponifica- Percent AcrdValuc,

Neutral mg. KOH/g.

011 Parts in KOI-I g. tion Value, on g mg./KOH/ Oil Eng. trained 7 1.30160 196 0. 0. 05 Nil 3.16 114 196 1. 32 0.

In this example the refining factor may readily be calculated asfollows:

weight of substances recovered from the oil weight of free fatty acidsoriginally present in the oil Refining factor (R.F.)=

The weight of substances removed from the oil when the SXS is present is1.30 parts and the weight of free fatty acids in the original oil is1.10 parts (half the acid value of 2.2 mg. KOH/g.).

Where no SXS was used the refining factor is The advantages of theprocess can also be shown by reference to calculated values of thepercentage of neutral oil entrained in the aqueous layer. These figuresmay be calculated by two methods, as follows:

(i) The extra weight of crude fatty acid obtained i.e. weight of crudefatty acids obtainedweight of fatty acid originally present, per partsof crude oil. This method gives the correct result only if there hasbeen no hydrolysis of the oil during refining.

(ii) Since the acid value of the crude fatty acids is a measure of theactual fatty acid content thereof the ratio acid value (AV) fatty acidsaponification value (SV) fatty acids +entrained oil per 100 parts ofcrude oil. Applying methods (i) and (ii) to the cited example 7% SXS NoSXS 1.30-1.l=0.20% 3.16-1.10=2.06%

The coincidence of the results obtained by method (i) and method (ii) inthe SXS refining is yet another measure of the superiority of theprocess. This shows that all of the acid ending up in the crude acid oilwas originally present as fatty acid in the oil.

In the conventional refining experiment the two figures areinconsistent, and since method (i) relies on there being no more acidpresent in the system at the end of the refining procedure than at thestart, method (ii), which relies only on measured quantities, applies,and shows that more acid is present at the end, i.e. hydrolysis hasoccurred during the refining.

Since the refined neutral oil in the conventional process still contains0.13% fatty acid (the equivalent of an acid value of 0.25 mg. KOH/g.),only 0.85% (Ll-0.25) of the original fatty acid is transferred into thecrude fatty acid. Since 3.16% of crude fatty acid is obtained, then2.31% (3.16-0.85) of oil is entrained, either as acid produced byhydrolysis or as oil. Thus the loss of oil is even greater than at firstsight appears, due to the relative inetficiency of the conventionaldeacidification.

EXAMPLES 2-12 The quantity of oil stated in Table 2 was heated to 90 C.and treated while stirring with a solution of SXS (4X percent FFA) andsodium hydroxide of theory) in water such that the final Halvoponconcentration was 40%.

After the times shown, the lower aqueous layer was separated, acidifiedto pH4 with 70% sulphuric acid and the separated acid oil washed withwater and dried.

The neutral oil layer was washed twice with water and vacuum dried.

TABLE 2 Neutral Oil Acid 011 Time of Example Oil Percent Wt. crudeRefining Separation F oil Wt. Percent Percent Wt. AV SV Factor (mins)FFA Soap 2 Peruvian Fish. 0. 05 1. 16 40 a 0.2 1.00 45 Fish (Herring)0.05 1.00 40 5..- Crude Hardened 0. 05 1. 11 35 Fish Oil. 6 Tallow 471 g230 g 1.1 0.6 1.23 45 Coconut"... 1,170.5 g 1,067 g 056 0. 084 l. 18 30Sunfiower. 3,267 g. 3,232 g. 0.008 0. 042 1.00 35 Rice Bran 400 g 161g 1. 27 O. 28 1.16 45 Rape 000g s73 0.14 0. 07 1.25 40 Soya Bean..- 500g 495 0.07 0. 1.38 40 12 live 1,000 g 886 g 0.12 0.05 1.00 35 EXAMPLE'13 The results are summarised in Table 3.

Crude snufiower seed oil (10,000 kg.) was treated at TABLE 3 50 C. with60% phosphoric acld (100 kg.), the tem- Neutralon Acid Oil Refiningperature ralsed to 90 during 30 minutes with stirring, and Y. m P m v Pfactor the mixture allowed to separate for 1 hour. The aqueous i r ii(1% g.) A W l r i phase was discarded, the oil washed with water (400kg),

f 5 000 k h Ontaim A 4,792 0.08 185 75 188 39.8 8.1 and dlVl ed into twoportions 0 g. eac c 4,922 Q06 76 166 189 8&0 1.17

ing 1.34% FFA.

Portion- A The degummed oil (5,000 kg.) was neutralised in theconventional manner at 70 C. with sodium hydroxide (67.2 kg. of 15%solution). The mixture was stirred for minutes after alkali additionthen allowed to separate for four hours.

The aqueous soapstock layer was removed and the oil washed with water(200 kg.). It was necessary to repeat this operation a further 14 timesto bring the soap content of the neutral oil below 0.05%.

The yield of neutral oil after vacuum drying was 4792 kg, thus therefining loss was 208 kg. giving Refining factor= In connection withthis example it should be noted that a lower temperature was requiredwhen no SXS was present, since in the absence of SX'S there is a greatertendency of the alkali to hydrolyse the oil.

Herring oil (5.65 %FFA) was used in the following examples.

The oil -('100 g.) was stirred at 90 C. with a solution of 34 g. of thesulphonate salt (equivalent to 6 FFA) together with 0.88 g. of sodiumhydroxide (equivalent to 110% of theory) in water, (51 g. in Examples 14and 15, 80 g. in Examples 16 and 17, corresponding to 40% and 30%solutions of sulphonate salt respectively).

After separation (maximum 30 minutes) the neutral oils were separatedand analysed. The soapstocks were split with sufficient 70% suphuricacid to give a pH of 4, and the acid oil recovered, washed dried andanalysed.

TABLE 4 Neutral Oil Acid Oil Refining Example Sulphonate Salt FactorWeight Percent Percent Weight AV S FFA Soap We claim:

The neutral oil had an FFA content of 0.08%.

The soapstock was acidified to pH4 with 70% sulphuric acid causing aseparation of acid oil. The acidic aqueous layer was run off, the acidoil was Washed with water kg.) and dried.

Portion B The degummed oil (5,000 kg.) was heated to 93 C. and treated,with stirring, with a solution of sodium hydroxide, (9.5 kg.) andHalvopon OR (202 kg.) in water (2885 kg). After stirring for 10 minutesthe mixture was allowed to separate for 20 minutes.

The lower aqueous phase was run 011 and the neutral oil washed withwater (3 X 200 kg.) giving a soap content in the oil of 0.04%.

The oil was vacuum dried and weighed, giving 4922 kg. with an FFAcontent of 0.06%. The refining factor calculated as for A is 1.17.

The soapstock was treated as in A.

1. In a process for refining crude vegetable, animal and marine oilsconsisting of neutral glyceride esters of fatty acid containing fattyacid impurities which comprise refining said crude oil at a temperatureabove the melting point of said crude oil by admixing with said crudeoil an aqueous solution of an alkali thereby forming an oil phase and anaqueous soap phase, and separating the aqueous soap phase from said oilphase, the improvement which comprises admixing with said crude oil andsaid aqueous alkali, a salt of a sulphonic acid selected from the groupconsisting of mononuclear aryl or alkyl mononuclear aryl sulphonic acidswherein the aromatic nucleus may contain up to three alkyl substituentsand the total number of carbon atoms of all the alkyl substituents doesnot exceed four, the concentration of the sulphonic acid salt being atleast 30% by Weight based on the total amount of water present.

2. The process of claim 1 wherein said salt is an alkali metal orammonium salt of at least one sulphonic acid selected from the groupconsisting of benzene, xylene, toluene and cumene sulphonic acids, saidsalt being present in an amount between about 2 and 6 times the weightof the fatty acid present in said crude oil.

3. The process of claim 2 wherein the concentration of said sulphonicacid salt is between 40% and 60% of the weight of the water present.

4. The process of claim 1 wherein the concentration of said sulphonicacid salt is at least 40% by weight based on the total amount of waterpresent.

5. The process of claim 4 wherein said sulphonic acid salt is a salt ofan alkali metal.

6. The process of claim 5 wherein said salt is at least one sulphonicacid selected from the group consisting of benzene, xylene, toluene andcumene sulphonic acids, and wherein said sulphonic acid is present in anamount between about 40% and 60% of the weight of the water present.

7. The process of claim 6 wherein said salt is a salt of Xylenesulphonic acid.

8. The process of claim 7 wherein said salt is a sodium salt, and ispresent in an amount between about 2 and 6 times the weight of freefatty acid in said crude oil.

9. In a process for refining crude vegetable, animal and marine oilsconsisting of neutral glyceride esters of fatty acid containing fattyacid impurities which comprise refining said crude oil at a temperatureabove the melting point of said crude oil by admixing with said crudeoil an aqueous solution of an alkali thereby forming an oil phase and anaqueous soap phase, and separating the aqueous soa-p phase from said oilphase, the improvement which comprises admixing with said crude oil andsaid aqueous alkali, a salt of cumene sulfonic acid, the concentrationof said salt of cumene sulfonic acid being at least 25% by weight basedon the total amount of water present.

10. The process of claim 9 wherein said salt is an alkali metal salt.

References Cited UNITED STATES PATENTS 3,065,249 11/1962 Repapis260-42'5 ALEX MAZEL, Primary Examiner.

A. M. T. TIGHE, Assistant Examiner.

